The present invention relates to a concrete admixture.
A highly strong concrete is promoted to be used in order to correspond with a multistoried building or a large construction in recent years. For these, a concrete admixture is required to have a flowability in an application of a concrete paste as well as to have an ability of highly reducing water from the concrete paste and another ability to reduce a viscosity of the concrete paste being sent under a pumping pressure.
There was a high water-reducing agent for a highly strong concrete such as a condensate of naphthalenesulfonic acid with formalin (i.e. a naphthalene-based compound) and a condensate of melaminesulfonic acid with formalin (i.e. a melamine-based compound), up to now. In addition, there is recently known a water-soluble vinyl-copolymer (e.g. a polycarboxylic acid-based compound) exhibiting an excellent dispersibility (slump value) such as a copolymer of polyalkylene glycol monoester-based monomers with (meth)acrylic and/or dicarboxylic acid-based monomers. However, although the dispersibility is improved by the water-reducing agent among them, the flowability of the concrete paste is poor after being send under the pumping pressure so that the applicability of the concrete paste is unsatisfactory.
JP-A 59-18338 or JP-A 8-12396 discloses a prior method for producing a polycarboxylic acid-based copolymer. That is, monomers are uniformly added in the prior method. However a mixture of the obtainable copolymers is unsatisfactory in the dispersibility and flowability. Although JP-A 8-59323, JP-A 7-118047, JP-A 5-24894 or JP-A 61-31333 provides another polycarboxylic acid-based copolymer, the ratios of monomers are not changed at admixing the monomers in its producing method. Accordingly the copolymer is unsatisfactory in the dispersibility and flowability. Further, for example, JP-A 9-40446 corresponding to EP-A 983976 provides a concrete admixture comprising two copolymers being different from each other in the ratios of monomers, but a mixture of the copolymers is also unsatisfactory in the dispersibility and flowability.
The object of the present invention is to provide a concrete admixture which is particularly useful in the field of highly strong concretes, which has a high dispersibility and flowability and which is excellent in an applicability of concrete.
The present inventors have found that a mixture of copolymers obtained by reacting specific monomers preferably in a specific molar ratio is effective for solving the problem described above. As the result of their further examination on the basis of this finding, they have found that there is particularly effective, among mixtures of such copolymers, a mixture of copolymers obtained by changing a molar ratio of (raw) monomers in the copolymerization course or there is particularly effective another mixture of at least three copolymers obtained by respectively copolymerizing mixtures in molar ratios being different from each other. Thus, the present invention was thereby completed.
That is, the present invention relates to a concrete admixture comprising a copolymer-mixture obtained by copolymerizing at least one monomer (A) represented by the following formula (a) and at least one monomer (B) represented by the following formula (b), changing a molar ratio of the monomer (A) to the monomer (B), namely (A)/(B), at least one time in the polymerization course [,which is referred to as the concrete admixture (I) hereinafter]: 
wherein
each of R1 and R2 represents a hydrogen atom or a methyl group,
m is a number selected from zero to 2,
R3 represents a hydrogen atom or xe2x80x94COO(AO)nX,
p is zero or 1
AO represents an oxyalkylene group having 2 to 4 carbon atoms or an oxystyrene group and preferably an oxyalkylene group having 2 or 3 carbon atoms,
n is a number selected from 2 to 300, and
X represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms and preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; and 
wherein
each of R4, R5 and R6 represents a hydrogen atom, a methyl group or (CH2)m1COOM2, in which (CH2)m1COOM2 may be cooperated with COOM1 or another (CH2)m1COOM2 to produce an anhydride, in this case, M1 and M2 in these groups are not present,
each of M1 and M2 represents a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group, an alkylammonium group or a substituted alkylammonium group, and
m1 is a number selected from zero to 2.
Further, the present invention relates to a concrete admixture comprising a copolymer-mixture of at least three copolymers obtained by copolymerizing at least one monomer (A) represented by the formula (a) and at least one monomer (B) represented by the formula (b), changing a molar ratio of (A) or (B) respectively at another molar ratio of (A) to (B), namely (A)/(B), in the range of 0.02 to 4, provided that the formulae (a) and (b) being defined above [,which is referred to as the concrete admixture (II) hereinafter].
Further, the present invention relates to a concrete composition comprising at least one of the concrete admixtures (I) and (II) described above in the present invention.
The present invention also provides a concrete composition comprising aggregates, cement, the concrete admixture as defined above and water; use of the copolymer-mixture as defined above as a concrete admixture; a method of dispersing aggregates, cement and water with the copolymer-mixture as defined above; a process for producing a copolymer-mixture, comprising copolymerizing at least one monomer (A) represented by the formula (a) and at least one monomer (B) represented by the formula (b), changing the molar ratio of (A) to (B), namely (A)/(B), at least one time in the copolymerization course, provided that the formulae (a) and (b) being defined above; the above mentioned process wherein the molar ratio of (A) to (B), namely (A)/(B), is changed at least two times; use of the copolymer-mixture as obtained by the process shown above as a concrete admixture; and a method of dispersing aggregates, cement and water with the copolymer-mixture as obtained by the process shown above.